Light diffusing apparatus is often used in visual indicators, for example in telephone sets, to indicate that a message has been left by a calling party. Known visual indicators may include an elongate window which transmits the light supplied by a spot source such as a lamp or light emitting diode. However, the window material of these visual indicators does not diffuse the light evenly so as to provide equal brightness throughout the window. This results in a bright spot which appears relative to the position of the lamp in the visual indicator. Other uses of such visual indicators are, for instance, in video cassette recorders and radios.
U.S. Pat. No. 4,989,933 granted to Duguay et al on Feb. 5, 1991 discloses a light guide resonator to produce uniform diffuse light. The light resonator includes reflecting mirrors, a flat and polished transparent slab and a light-diffusing layer which are located at the one end of a light guide. Despite the fact that the light resonator is stated to produce uniform diffuse light by means of light resonation, the resonator is of large and complicated structure and it would be difficult to use effectively on small household items, such as telephones, video cassette recorders, radios, or telephone answering machines.